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| Home > Publications database > Sequential and coupled inversion of time-lapse borehole GPR measurements for vadose zone model parameterization |
| Book/Dissertation / PhD Thesis | FZJ-2022-01999 |
2022
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-607-6
Please use a persistent id in citations: http://hdl.handle.net/2128/31076 urn:nbn:de:0001-2022051802
Abstract: A profound understanding of the infiltration dynamics into the vadose zone is crucial to ourcapacity to link surface and subsurface processes for the description of the hydrologic cycle. Akey to establish reliable models describing the infiltration process is the knowledge of the soilhydraulic parameters. A promising approach to estimate soil hydraulic parameters is inversemodeling based on dynamic changes in soil water content (SWC). In this context, groundpenetrating radar (GPR) has been recognized as a powerful geophysical technique in vadose zonehydrogeophysics, because SWC is strongly related to the soil bulk permittivity that can beprecisely determined by GPR. The aim of this thesis is to investigate the feasibility of using timelapseGPR measurements obtained during infiltration events for vadose zone characterizationwith a special focus on the estimation of soil hydraulic parameters.A prerequisite for estimating soil hydraulic parameters based on GPR measurements obtainedduring infiltration events is that the GPR measurements should reliably reflect the transient SWCdynamics during and after infiltration events. To verify this, a 4-day infiltration experiment wasperformed at the rhizotron facility in Selhausen, Germany. SWC information at 0.2, 0.4, 0.6, 0.8,and 1.2 m depths were obtained by zero-offset profiling (ZOP) measurements from horizontalborehole GPR. Unfortunately, SWC information for the top 0.1 m of soil obtained by ZOPmeasurements was not reliable due to the strong interference between direct and refracted waves.To solve this problem, surface GPR measurements were additionally conducted. Dispersiveguided waves were observed in the 500 MHz surface GPR data because the infiltration eventgenerated electromagnetic waveguides in the top soil layer. This allowed to obtain SWCinformation of the top 0.1 m soil layer through dispersion analysis of the dispersive surface GPRdata. By combining surface and horizontal borehole GPR measurements, the vertical SWCprofiles (0 - 1.2 m) and dynamics were successfully represented during and after infiltration events.Additionally, it was found that the GPR-derived SWC corresponded well with independentlymeasured SWC estimates obtained with time domain reflectometry (TDR) and the known amountof water applied in the infiltration events.
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